I did the exact same thing. I placed a FORD 190 in and while towing a 1500# tent trailer on the freeway the Temp would be on the high side of the M. Drove back home and placed a 180 and the temp stays between N and O. Heater works fine. thx jc

 

I had a similar problem on mine,was the clutch fan ,easy enough to change if not that you might have an air lock in the system run it for a bit and grab the heater hoses see if they are hot if one is hot and not the other could be either a plugged heater core or a sticking hot/cold valve or even a air lock (as stated earlier) in the heater core.In any event i would give the system a good flush dont know if you got one of those garden hose connections on your heater lines but there a cheap & easy way to flush your system.OH by the way the valve mentioned by me and others on this thread is located directly back from the heater core on the heater lines it is controlled by vacuum to switch from hot air to cool air ...Hope this of some help,lets us know your progress.. >>>>BOB

 

That valve only exists on later Aerostar models. I have a '93 and it doesn't have it. My '95 has it, though. I don't know about '94, maybe someone else can tell us?

Also, the temperature gage is for real, not just an idiot gage. The sender is actually a thermistor with a Beta coefficient of about 3500. I did take it out of the van and measured it at different temperatures. At room temperature, the resistance is about 370 ohms, and at water boiling temperature it is 27 ohms. If you splice a wire onto the wire that plugs into the sender, you can see the voltage change as the engine heats up. At normal operating temperature, it reads about 2.4 Volts versus 5.0 Volts when cold. The signal is extremely noisy, however, since the gage is inductive and any slight motion would cause lots of noise on that line.

The problem is that the sender has to be replaced periodically also, depending on how much vibration you have on the engine. The thermistor element inside the sender is bonded on and might come loose. When it does, it reads lower than actual temperature.

Regards

 

My 94 has it ,sorry i misread your year >>>90 4.0L to be 94 _OOps!!,thats weird though how does it change between hot & cold air if theres no valve i could see if it were in a different place maybe,anyways the other info should still apply.my temp gauge on my 94 never gets above the n in normal sometimes it just rides on the C in COLD>Lots of heat still.

 

That's an easy one. The core is always hot. When you move the temp selector the air either goes through the heater core or goes around it or a mix. Thus various temps by moving the temp selector.

In the newer (94+) models, what the valve does is stop any hot water going through the heater core when you are in A/C mode. It helps the A/C a little. Nice idea, just don't know how noticable the difference is.

 

I think the hot/cold air is selected by a vacuum actuated door inside that huge ugly box on the firewall. The valve only controls the water flow through the heater core, and that was added in later models. Why? I have no idea

 

Ok, you say the radiator hose never gets hot, in Florida? In the summer? It must be the thermistat is not fully closing. If this happens it will never warm up.

 

Sorry, I've been busy painting the house and have not had time to respond. 1st, 90's don't have the bi-pass valve to block the heat from the heater core. Used in later models.

2nd, the water temp in the summer is still cool enough to hold the hoses and touch the radiator. The heater air inside is very lukewarm and will not get hot even though there is sufficient air flow. Touching the cover on the heater core is luke warm also.

The troubling part is the way the temp acts. At startup, the temp will very slowly climb from cold to the N in normal on the guage. Almost as soon as it gets to the N it immediately drops to the cold bottom again. Then, for as long as it is running It will once again climb to the N and then immediately drop to the bottom again. This happened before I changed the thermostat and after, even on the hotest days.

Living in Florida, this has not been a bad thing, except on the rare, cold days we get here. But with plans to move north soon, this is no longer a good thing. I suppose I am going to need to try the 190 degree thermostat from Ford and see what that does. The thermostat I have must be opening and closing or I would not see the dramatic temp changes.

Thanks everyone for the info.

John

 

I would say that the thermostat change should do it. The Ford themostat up in Canada, at least in Alberta, is a Bosch part. This solved my engine temp problem as stated earlier. I believe that the 4.0 L motor is German so that may be why it is a Bosch part.

 

When I was using a Stant 180° the temp gauge needle reached to arrive "A" exactly;. Now I am using a 180° RoadStar thermostat and the needle arrives until the letter "R" when engine is very hot.
I believe that temp gauge works according to the factory that makes the spare parts and the degrees of thermostat.
Greetings